The present invention relates to methods for fabricating semiconductor devices; and, more particularly, to methods for forming ferroelectric capacitors.
Memory elements (FRAMs) using ferroelectric capacitors store information by switching capacitors as different from DRAM elements. Thus, the ferroelectric having switching property such as PZT and strontium bismuth tantalate (hereinafter, referred to as SBT) has been used as a dielectric layer of capacitors in the memory elements as different from DRAM using common dielectric. However, the ferroelectric layer is contacted with silicon dioxide containing many hydroxyl groups at the process of planarization after capacitor forming process. Accordingly, there is a drawback in the prior ferroelectric capacitors that such hydroxyl groups react with the ferroelectric such as PZT and SBT, thereby decreasing the characteristics of the ferroelectric by its reduction.
It is, therefore, an object of the present invention to provide methods for forming ferroelectric capacitors which can prevent the decreasing of the characteristics of the ferroelectric by blocking the reaction of the ferroelectric layer with hydroxyl group induced from the layer of inter-layer insulator which is formed after the formation of the capacitor and contacted with the ferroelectric layer.
In accordance with one embodiment of the invention, there is provided a method for forming ferroelectric capacitor, which comprises the steps of: forming a lower electrode over a semiconductor substrate; forming a layer of ferroelectric material on said lower electrode; forming a layer of ZrO2 as a diffusion barrier which encloses portions of said ferroelectric layer other than a portion through which the ferroelectric layer will be connected to an upper electrode; forming said upper electrode to connect to said ferroelectric layer.
In accordance with another embodiment of the invention, there is also provided a method for forming ferroelectric capacitor which comprises the steps of: selectively etching an insulating layer formed over a semiconductor substrate so as to expose said substrate or a predetermined conductive layer, thereby forming a contact hole; burying conductive material in said contact hole to form a first conductive layer; forming a first diffusion barrier layer over the entire substrate; forming a second conductive layer for forming a lower electrode over the entire substrate; forming a ferroelectric layer on said second conductive layer; patterning said ferroelectric, said second conductive and said diffusion barrier layers; forming a second diffusion barrier layer over the entire substrate so as to enclose said ferroelectric layer; selectively etching said second diffusion barrier layer to expose said ferroelectric layer in the portion which will be contacted with an upper electrode; forming said upper electrode so as to connect to said ferroelectric layer.
The invention enhances the characteristics of the ferroelectric capacitor by forming the diffusion barrier layer using the insulating and diffusion barrier materials such as ZrO2, Y2O3, CrO2, CeO2, ZrN and TaN to prevent the damage of the ferroelectric layer due to the hydroxyl group generated when an oxide layer is formed as an inter-layer insulator after the formation of the ferroelectric layer such as Pb(Zr,Ti)O3 (PZT).